Which of the following would be the best location for a wind farm with ten industrial turbines?

4.12 Advantages and disadvantages

Abstract

Wind energy, which is produced by wind power, refers to the process of creating electricity using the wind, or air flows that occur naturally in the earth's atmosphere. Modern wind turbines are used to capture kinetic energy from the wind and generate electricity. A windmill converts the energy in wind into electrical energy or mechanical energy to pump water or grind cereals. The most common windmills in operation today generate power from three-blade, horizontal-axis windmills with the nacelle mounted on steel towers that can be cylindrical steel plate or lattice towers. This modern windmill concept has grown since 1977 and has become the industrial standard.

POTENTIAL FOR WIND IN THE USA

Currently wind energy produces only 0.1% of the nation's electricity, but it could produce a significantly greater amount during the next decade. The US Department of Energy estimates that by the year 2000 wind – with business as usual – could supply 10 times more electricity than produced in California today.31 Even in California there remains ample undeveloped wind resources. The CEC has identified more than 7 000 MW of prime wind resources, only a portion of which has been developed.32

The Great Plains contain tremendous potential. One ridge in southwestern Minnesota alone could produce as much wind-generated electricity as that produced in all of California today. And just one site in Montana could provide 17 times California's current wind generation. Battelle Pacific Northwest Laboratories, in a recent report, calculates that there are sufficient wind resources in the contiguous USA to meet 27% of the nation's electrical consumption even after removing many areas because of potential land-use conflicts. Battelle's study assumed the ability to ecnomomically-use only class 5 (7.5–8 m/second annual average wind speed) or windier resources, under moderate environmental restrictions (Figure 15).33 But Class 4 (7–7.5 m/second) resources are currently being used in Denmark and Germany. If Class 4 resources were tapped in the USA, wind alone could meet the nation's total demand for electricity. In a realistic scenario, wind energy could meet 10% of the nation's electricity supply sometime after the year 2000.

1.6 Summary

In this chapter, wind energy as well as its advantages and disadvantages are explained. Different wind turbines are introduced, and for an HAWT, different parts are discussed. It is good to mention that VAWTs also have the same components, and only the design differs. For example, the gearbox, generator, wind speed sensors, and many other components also exist in VAWTs. However, some parts may not be needed. For example, wind direction is not important for VAWTs. As another example, VAWTs usually are not mounted on a tower.

This chapter summarises developments in contemporary wind energy. The review will cover: the global resource and its assessment; wind turbine technology and its recent up-scaling and evolution; offshore prospects and engineering challenges; and the research required to underpin these developments. The growing issues surrounding the integration of an increasing proportion of wind generation into power systems will be discussed in some detail as they are of increasing concern to power system operators. This discussion will touch upon other generation technologies and their strengths and weaknesses in the context of a move to clean and sustainable electricity generation.

Abstract

In this chapter, we embark on the study of wind energy, which has the potential to contribute significantly to meet humanity's power generation needs. After covering some historical aspects and learning a basic classification of turbines, we will focus on how are wind resources are measured and on how we can estimate the probability of having winds with speeds that exceed a certain value at a location of known mean wind speed. We will learn how to quantify the power density in the wind and the fraction of it that is available for power conversion. At that point, we will be ready to explore the fundamentals of wind turbine analysis and learn key aspects of turbine design, including considerations of airfoil geometry and the forces that result from the interactions between the wind and the turbine blades.

5.3.4 Predicting wind energy

The intermittent nature of wind makes it necessary to look for a possible way to forecast wind energy. This forecasting is different from wind energy estimation in the sense that the former relates to the wind speed prediction at any time. Whereas energy estimation provides the potential of wind energy related to that area. Wind energy-related scheduling and energy dispatch is improper so far, hence the prediction can help the overall system in several ways, including efficient scheduling for wind energy accommodation, better economic constraints, and allows the stakeholders to look for alternate options to avoid penalties. Many sophisticated high-accuracy models have been developed for wind speed prediction [29–33]. Many are already in use by different wind energy producers.

16.4 Sustainability attributes

Wind energy is a freely available renewable energy source, which has been in the focus of humankind for centuries. Evidently, capturing this free energy (which is initiated by the solar radiation and hence is unlimited on the humankind time scale) is one of the best solutions for sustainable development. In this regard, wind power generation has enjoyed enough investment into research, development, construction, and the special regulations and economic incentives. This has resulted in an ongoing growth of the installed capacity, increase of efficiency and size, and development of new technologies like floating wind turbines to capture more wind resources of higher quality.

Evidently, wind power generation has a number of valuable advantages [6], for instance:

The amount of lifetime GHG emissions associated with wind turbine technology is limited to the production, transportation, and erection of the wind farms, and is the lowest compared to other technologies. According to the studies [20], wind has among the lowest lifecycle CO2 equivalent emissions at the level of 2.8–7.4 g per kWh of generated electricity. Wind energy is also free from particulates or sulfur dioxide, which are considered a major problem of coal-fired power plants.

Wind energy is fully sustainable as it is kind of “solar” energy: whenever the sun shines and therefore the wind blows, energy can be harnessed and sent to the grid.

Wind turbines have a small footprint and thus can be combined with other activity like farming and growing crops. They can be located in remote locations or mountainous regions where winds are strong but the location does not allow any other activity.

Wind resources are distributed more evenly throughout the countries compared to fossil fuels, hence they can contribute to national energy security on a higher level.

Compared to any type of thermal energy or biomass, a wind power plant consumes very limited water resources, roughly 170–320 l per kWh of generated electricity [6]. This is especially important in the face of growing fresh water scarcity and water conservation problem.

As for any other technology, there are still some limitations that may impact the deployment of wind power generation. These are, for instance:

The intermittency of wind does not allow the wind farms to generate stable base load electricity. Therefore, integration of wind parks requires extra capacities to compensate for losses of wind and shutdowns through primary and secondary reserves. For the moment, these are done by gas turbine driven power plants (usually simple cycle, however, modern combined cycle can also propose fast ramp up and flexibility rates) or hydropower.

Good sites are usually in remote locations, while the easily accessible sites have already been used for wind generation.

Shortage of rare earth element, neodymium (Nd), needed to manufacture permanent turbine magnets. Wind turbines containing such magnets manufactured out of neodymium, iron, and boron (NdFeB) have demonstrated a series of advantages in terms of efficiency, weight, dimension and maintenance, which are key requirements in wind applications, especially for offshore [21]. These permanent magnets, which are much stronger than traditional iron magnets, are required in the generator to produce electricity at slow rotation speed. At the moment, the supply of neodymium has been dominated by China with the US now reopening their mines [6]. The direct substitution of rare earth materials like Nd in permanent magnets or the development of new materials with a similar functionality to the NdFeB magnet is still at the research stage. However, progress has recently been made on magnet manufacturing techniques and wind generator design that allow the reduction of the amount of rare earths used in a wind turbine [21].

It is almost generally accepted that the utilization of renewable energies is, besides energy saving, the best means to reduce pollution and decelerate climate change, and wind energy has proved its efficiency and positive contribution to combat climate change. On the other hand, there are still some issues regarding the environmental impact in a broad sense [22]:

Noise emissions due to the aerodynamics of the wind mill, especially of the rotating blades. Besides noise in the audible frequencies so-called infra-noise has also been the subject of concern [22].

Oscillation shadow due to the rotating blades causes optical disturbance for the residents. Depending on the local conditions, minimum distances may be required by the regulation.

Impacts of wind energy development on wildlife can be direct (collision fatality) or indirect (functional habitat loss or barriers to movement). The mitigation strategies may include careful site consideration, repowering of sites (replacing smaller old units with larger ones as the latter decrease the mortality rate by more than 50%), curtailing operations at high-risk periods for birds, or using special sound devices or visual approaches (applying paints on blades) to warn birds [23].

Visual appearance and disturbance of the landscape, especially in tourist popular areas.

Still, wind energy is a growing contributor to sustainable power generation system. It has also shown its credibility within hybrid installations, particularly with solar PV or hydroenergy. Used on industrial scale, wind energy has been supported by the developed regulation, and recent projects have demonstrated its economic advantage over conventional competitors.

Land Use Issues

A wind farm requires roughly 0.1 km2 (0.039 sq mi, 25 acres) of clear land per megawatt of turbine capacity. A 1-GW (1000-MW) wind farm, for example, might extend over an area of approximately 100 km2 (25,000 acres). If they are sited closer together, the turbines start to interfere with each other’s efficiency and they begin to harness less energy. 1 GW per 100 km2 amounts to 10 W/m2, and that is the maximum energy that can be harnessed if the wind blows at a constant rate all the time. If you put larger turbines in the same area, you have to put them farther apart so that they do not interfere with each other. The area required per turbine increases linearly as the turbine power increases. The maximum recoverable wind energy, however, remains constant at 10 W/m2. Moreover, the average capacity factor for modern wind turbines is about 20%-30%, so this means that the turbines can harness about 2-3 W/m2 (Figures 9.8 and 9.9).

In a typical wind prone area, the total available power from the wind is about 500 W/m2. It would appear that wind turbines are capable of capturing less than 1% of this energy. It is not possible to harness more than 3 W/m2 from even the most favorable windy areas. This may seem like a relatively large footprint for an energy harnessing installation, but the land can still be used for other activities, particularly crops and animal grazing. Wind energy experts contend that less than 1% of the land needs to be used for foundations and access roads; the other 99% can still be used for farming. Some clearing of trees around tower bases would be necessary for the installation of tower sites in wooded areas, but the affected footprint would remain small.

At 2-3 W/m2, the current installed wind-generating capacity of 46 GW occupies an area of 15-23 Gm2 (3.7-5.7 million acres). If you wanted to increase production to 200 TWh/month—half of the U.S. electricity demand—you would need to install another 875 GW of wind-generating capacity for a total capacity of 920 GW. This would occupy 310-460 Gm2 (76-115 million acres). This is approximately equal to the entire states of Colorado and Nebraska combined. While it is feasible to do this, the 875 GW would have to be backed up by other energy sources or energy storage capacity.

Figure. 9.10 shows the average wind speed in all areas of the United States. The best areas for wind power generation are in the central plains areas reaching from North Dakota and Montana in the north to Texas in the south, to Wyoming in the west, and as far east as Indiana. There are clearly large areas of the country that are suitable for wind generation. This map does not include offshore areas where additional potential exists.

In the United States, landowners typically receive $3,000 to $5,000 per year in rental income from each wind turbine, depending on the size. These turbines are usually deployed at a density of about one every thirty acres. A 1,000 acre tract of land, for example, could generate about $100,000 per year for the landowner in addition to the income gained from growing crops or grazing animals on the land.

Turbines are not generally installed in urban areas, except as smaller single units (see Figure 9.11). Buildings interfere with the wind flow, and turbines must be sited a safe distance from residences to guard against failure. The 20-MW Steel Winds project south of Buffalo, New York is an exception. It is situated in an urban location, but is separated from residences by siting the turbines on an uninhabited lake shore.

Wind turbines located in agricultural areas do interfere with crop-dusting operations. Operating rules prohibit the approach of aircrafts within a stated distance of the turbine towers. Even if turbine operators agree to shut down the turbines during crop-dusting operations, flying between turbines is still hazardous and limits the effectiveness of crop dusting.

In Ireland and Scotland, there has also been concern about the damage caused to peat bogs, with one Scottish politician campaigning for a moratorium on wind developments on peat areas claiming that, “Damaging the peat causes the release of more carbon dioxide than wind farms save.”

Wind energy

Wind energy is the second most significant renewable technology after hydropower in terms of electricity production. Global output from onshore wind turbines in 2019, according to the IEA, was 1202 TWh while offshore wind farms provided a further 66 TWh, for a total of 1268 TWh. Meanwhile figures from the Global Wind Energy Council (GWEC)12 indicate that total installed capacity for wind energy in 2018 was 591 GW, of which 568 GW was onshore and 23 GW was offshore. The total capacity rose to 651 GW at the end of 2019.

Wind energy, the energy contained in a mass of moving air, is available in most parts of the world but the size of the resource will vary from place to place depending on the wind regime. Wind energy can be harvested on land and at sea. The offshore resource is generally the most consistent, the most reliable and able to supply the highest energy intensity. Onshore wind resources are more variable because the wind must travel over a land mass and it will be affected by the contours of the land and by the ground cover. However all wind is dependent on the prevailing weather conditions and this leads to considerable variations in availability. Sometimes the wind blows intensely and sometimes it does not blow at all. This means that wind power is probably the most variable and the most unpredictable of all the renewable energy sources. Wind output reliability can be improved by coupling wind farms that are widely spaced geographically, in effect averaging output over a large area. Even so it is still possible for a whole region to become becalmed at times. Wind energy must therefore be supported by other forms of generation or by energy storage in order for it to provide a manageable resource. Wind and solar power can be complementary since the wind blows more strongly during winter while solar power is most intense during the summer. The management of wind output is one of the most challenging aspects of grid management today.

Wind energy is captured by wind turbines. When the wind industry was young, in the 1980s and early 1990s, there were a variety of wind turbine designs in use but the range has gradually narrowed so that today the market is dominated by a single type, the three blade horizontal axis wind turbine, with the turbine and its generator sitting on top of a tall tower. Wind strength increases with height so the higher the tower, the more energy can be collected at any given site. The sophistication and reliability of wind turbines has increased enormously since the pioneer days and new wind turbines can be expected to deliver power over a lifetime similar to that of other types of power generation.

There are two branches or families of wind turbines, onshore turbines and offshore turbines. Today the differences between the machines used for each are slight. Most significant is size, with offshore turbines tending to be larger than those used onshore. This is partly a matter of practicality. Transporting and erecting a very large turbine onshore can be very challenging in many locations whereas the are no limits offshore, provided only that vessels are available that can carry and install them. However, installation of turbines offshore is much more difficult than onshore and more costly. It is therefore more cost effective to install the largest turbine possible at an offshore site. Typical onshore wind turbines have generating capacities of up to 4 MW. Offshore, 6–8 MW is more typical of the capacity range, while turbines with generating capacities of 10–12 MW are expected to enter the market for the beginning of the third decade of the century. The main market for offshore wind is in European waters but China has been expanding its offshore wind capacity in recent years too.

The cost of wind energy has fallen dramatically over the last decade and over the 5 years to the end of 2019, the cost of both onshore and offshore wind had fallen on average by more than 50%, according to the GWEC. This has made onshore wind generation easily competitive in terms of cost with fossil fuel generating technologies and offshore wind is likely to be in the same position in the near future. Unfortunately the unpredictability of wind power often still leaves it at a disadvantage. One potential means of remedying this is to combine wind power with some form of energy storage. This will increase the overall capital cost of a facility but by increasing its reliability, makes the energy it produces more valuable. Various schemes are being explored including using offshore wind power to produce hydrogen which can then be shipped ashore and used as a green energy source.

The green environmental credentials of wind power make it attractive as a means of combatting global warming and most countries are building up wind capacity, some faster than others. However, it is not entirely benign. Onshore wind turbines are large additions to any landscape and they are not always welcomed by their human neighbours. This can be problematic when obtaining permits to construct wind farms onshore. There has also been an issue in the past with the danger of wind turbines to birds. However, the slow rotational speed of large modern wind turbines makes this less of a problem today. Noise, too, can be a problem onshore so it is not usually possible to erect wind turbines close to dwellings. Onshore construction is less of a problem in countries such as the United States and China where are wide expanses of uninhabited territory that can be used for wind generation. Offshore wind experiences few problems in this respect.